Apparatus for the washing of preferably cellulosic pulp

ABSTRACT

Apparatus for washing a suspension of a fibrous material as it passes through a container in which a washing liquid is passed from a supply chamber having a perforate wall into and through the suspension and then into a collecting chamber. Means are provided for interrupting the influx of washing liquid into the collecting chamber at suitable intervals by pressure variations in the liquid.

0 United States Patent 1191 1111 3,7 Leffler [45] May 1, 1973 APPARATUS FOR THE WASHING OF PREFERABLY CELLULOSIC PULP [56] References Cited [75] Inventor: Nils Gustav Lefiler, Sundsvale, UNITED STATES PATENTS Sweden 3,348,390 10/1967 R' ht ..68 l8l R 1 Asslgneer sunds Akt-ebolag, n mk. Sund- 1,214,152 1/1917 @2115: "21111412 x svall, Sweden 22 Filed; Man 17, 1971 Primary Examiner-William 1. Price Assistant Examiner-Philip R. Coe [211 App]' 125,349 Attorney-Pierce, Scheffler & Parker Related US. Application Data ABSTRACT [62] Division of Ser. No. 720,717, April ll, 1968, Pat.

103,622,261 Apparatus for washing a suspension of a fibrous I material as it passes through a container in which a 0 Foreign Application Priority Data washing liquid is passed from a supply chamber having 7 1 .A 1, ,1 r a perforate wall into and through the suspension and Apr. 13, 1967 Sweden ..5l83/67 then into 3 Collecting chamber Means are id for interrupting the influx of washing liquid into the [52] US. C1. ..68/l8l R collecting chamber at suitable intervals by pressure [51] hit. C1 ..D21C 7/00 variations i the liquid [58] Field of Search ..8/l56; 68/18 F, 181 R;

8 Claims, 5 Drawing Figures Patented Ma -1, 1973 [1* 1. FIG] llllllllllllllll I4 APPARATUS FOR THE WASHING F PREFERABLY CELLULOSIC PULP This application is a divisional application of my earlier filed parent application Ser. No. 720,717 filed Apr. 11, 1968, and now US. Pat. No. 3,622,262.

The present invention relates to an apparatus for the liquid treatment of suspensions of fibrous materials such as cellulosic pulp.

In the manufacture of bleached cellulosic pulp great advantages are obtained if, after one bleaching step, the pulp can be subjected to washing immediately in the bleaching tower instead of being washed on filters. A considerable advantage of this kind consists in that, after bleaching at about -15 percent pulp consistency, dilution of the pulp to about 1 percent consistency and a subsequent thickening of the pulp to about lO-l 5 percent consistency for the next bleaching step are avoided. One difficulty, both in connection with the washing of cellulosic pulp in bleaching towers and :in connection with other treatments of materials, in which liquid is caused to flow between chambers located below the level of material, has turned out to reside therein that, in particular, thesieve surfaces of the collecting chambers become gradually choked up during the withdrawal of liquor from the fibrous material (the fibers) that has to take place through said surfaces.

In order to prevent clogging of the sieve surfaces they have been made rotatable and for the purpose of cleansing sieve surfaces that have already become choked up, such surfaces .have been-adapted to be moved axially within the sieve chambers (Swedish Pat.

No. 198,496). However, the sieve chambers are both.

large and heavy the sieve elements usually have .a diameter of 4-5 meters and due to thisit would mean a great advantage if said elements could be made stationary and the possibility of keeping the sieve surfaces clean could yet bemaintained.

By means of the present inventionit has been possible to realize this desideratum. The invention includes a special arrangement, by which it is possible to keep stationary sieve surfaces free from clogging matter.

The new apparatus is meant for the treatment, by means of a liquid, such as water for washing (but also in connection with the displacement of liquor and dewatering) of a fibrous material suspended in a liquid... and being fed through a preferentiallyvertieal and preferably cylindrical container in the axial direction thereof, said treatment being carried out in that part of the container which is filled with the material, the treatment liquid being caused to flow throughthe suspension of material from at least one means of supply for the treatment liquid towards at least one collecting chamber for withdrawn liquid, said chamber having a foraminous, preferably perforate .wall. The new apparatus is characterized substantially in that the influx of the withdrawn liquid into the collecting chamber, is, entirely or partly, interrupted at suitable intervals in order to prevent clogging of the perforate wall of the collecting chamber and/or to facilitate the movement of the material past or along said surface. It is thought that this effect will be obtained thereby that the pulsatory flow will, inter alia, prevent fibers from getting stuck in the sieve holes, thus increasing the frictional resistance, and/or creating a film of liquid on the sieve surfaces in order to make it easier for the cellulosic pulp to slide past the same. Such film of liquid may also be obtained by spraying liquid along that sieve surface which is turned against the pulp and causing such spraying to take place in the same direction as the direction of feed of the pulp from one or more slots, located one after the other in the axial direction of the container all the way around along the sieve surface. An effective and correctly adjusted rinsing may result therein that the liquid in the collecting chamber inside the sieve plate member need not be pulsated, in which case the members serving that purpose may be dispensed with. The pressure variations are obtained through the intermediary of liquid, which by means of a vibratoror some other means, producing pulsations in the liquid, is pulsated within at least one conduit communicating with the collecting chamber. The pulsation of the liquid within the collecting chamber may be caused to take place either continuously or intermittently. Also,-to the liquid in the collecting chamber there may be imparted, at suitable intervals, one or more pressure surges and/or slower pressure rises. When performing the reciprocating flow the liquid should have a resultant flow into the collecting chamber for withdrawn liquid (the sieve device).

The apparatus comprises a, preferentially, vertical and preferably cylindrical container, adapted for axial feed therethrough of the material to be treated, at least one means of supply for treatmentliquid located within saidcontainer and below the intended level of material therein and furthermore at least one collecting chamber for withdrawn liquid arranged in a corresponding way but displaced in the radial direction of the container. The apparatus is substantially characterized in that to the collecting chambers for withdrawn liquidthere is connected at leastone member for transmitting pressure impulses to the liquid in said collecting chambers from means serving for generating pressure variations.

These and other characteristics of the invention will appear from the following detaileddescription of a preferred embodiment, reference being had therein to the accompanying diagrammatical drawing, in which FIG. 1 is a vertical sectional view of part of the apparatus, when mounted in a vertical container for the treatment of fibrous material,

FIG. 2, on a larger scale, illustrating a longitudinal sectional view ofthe means for pulsating the treatment li uid;

FIG. 3 is a sectional view on the line Ill-Ill of FIG. 1,

FIG. 4, a vertical sectional view of the collecting chamber and FIG. 5 is a cross sectional view of a second embodiment of the means for pulsating the treatment liquid.

Reference numeral 1 indicates part of the upper portion of a vertical, preferably cylindrical container, arranged to be traversed continuously by material to be treated, preferentially cellulosic pulp 2, in the direction indicated by capital A arrows. The treatment (washing) liquid is indicated by 3, and 4 is towerscrapingmeans, of a known kind, rigidly mounted on a rotary shaft 5. 6, 7 and 8 aresupply means for washing liquid and said means may be stationarily and/or rotatably mounted. Also,.they may be embodied in a known manner, for instanceas substantially vertically extending spray pipes or nozzles, which are movable along paths concentric with annular collecting chambers for withdrawn liquid in accordance with the disclosure of Swedish Pat. specification No. 198,496. 9 and 10 indicate collecting chambers for withdrawn liquid, said chambers preferably being devised as sieve baskets. One or more pipes 1 1 communicate with the collecting chambers 9 and 10, said pipes serving for leading away the withdrawn liquid by way of an overflow 12. H indicates the height of the static pressure determining the speed of flow of the liquid through the pipe 11. Also one (or more) pipe 13 communicates with the collecting chambers 9.and 10, said pipe 13 being, at its one end, by way of a funnel-like portion 14 connected to means 15 for generating pressure variations (a vibrator or a pulsator), which through the intermediary of that liquid which normally is to be present in the pipe 13 and in the funnel-like portion 14, are to produce a pulsatory flow of liquid through the slots or openings 16 in the walls of the chambers 9 and 10. In the embodiment shown the vibrator 15 comprises two centrifugal weights 18, adapted to rotate in opposite directions via gear drives 17. The vibrator is adapted to actuate a membrane 20, clamped between flanges 19, said membrane, by way of the liquid in the pipe 13, 14, transmitting the movements emanating from the vibrator, so that the previously mentioned, pulsatory flow through the slots 16 is obtained. The pipe 13 directs the pulsatory flow towards the sieve baskets 9, 10 and not towards the outlet pipe 11. Instead of the vibrator 15 there may be used some other means or some other member for generating the pulsatory flow of liquid through the slots or openings 16. Such other means may consist of, for instance, a piston 24 reciprocating in a housing 25, as shown in FIG. 5. The piston may be driven continuously or intermittently and its movements may be rapid or slow, even very slow. The use of a piston has proved particularly suitable for slow movements and long lengths of stroke or in case a rapid pressure surge is desired for the purpose of cleansing the slots or holes during the movement of the piston in one direction and in case a uniform and smooth withdrawal is desired during the return of the piston in the opposite direction. Consequently, in connection with this last mentioned functioning the piston is to move rapidly in one direction and then to return slowly in the other direction. The liquid within the housing of the piston may either be in a direct, open connection with the collecting chambers 9, 10 or in a power transmitting connection by way of a membrane or the like. After one single stroke, i.e., a movement in one direction, the piston may remain immobile in the end position for a certain period of time, alternatively its resting position may be occupied after one or more double strokes. 21 and 22 indicate supply conduits for washing liquid to the chamber 8 and, respectively, to the chambers 6 and 7. By way of control valves (not shown) said supply conduits are connected to a water conduit or to some other conduit, possibly also to a backwater conduit, i.e., in such a manner that the amount ofliquid and the pressure may be controlled. As shown, the conduit 21 ends above the arms of the tower scraping means 4. Treated material (washed pulp) leaves through the outlet 23.

In order that the material, for instance cellulosic pulp, shall be moved in the direction of the arrow A, Fig. 4 (i.e., upwards in the embodiment shown) it is required that the pressure p, be greater than the sum of the pressure p and the difference in static pressure between the levels p and p at friction-free flow. If the difference between these pressures is great the flow B of the displacement liquid may give larger inflow volumes at the lower portions of the sieve baskets (the collecting chambers) 9, 10 than at the upper portions.

According to the embodiment, shown in FIG. 3, the collecting chamber 9 is meant to have four outlet pipes, uniformly distributed along the circumference. All these pipes (with pipes between the collecting chambers) are indicated by 11. The collecting chamber 10 is meant to have two connections to pipes 11, counting along its circumference. The number of collecting pipes may be larger or smaller. A collecting chamber having a large diameter should have more pipes 11 than a chamber having a smaller diameter. Such pipes also may extend out of the tower, completely separated from each other. Theoretically, the pitch around the collecting chambers should be equal, irrespective of the diameters of the chambers. The same thing applies to the inlet pipes of the chambers 6, 7 for supplying the washing liquid. In these chambers the liquid should not have to be given a pulsatory motion, since the flow of liquid proceeds in a direction out of the chambers and the fibers of the cellulosic pulp should not have any tendency to cause clogging of slots or holes. Despite this fact it may, under certain circumstances, be of advantage to supply the chambers with intermittent pressure surges through the liquid in the supply pipe (pipes) and, under particularly difficult conditions, with continuous pressure surges.

The invention may, with advantage, be used also in such apparatus in which cellulosic pulp is dewatered from l-5 percent to about 8-15 percent in vertical containers with concentric sieve baskets arranged, in principle, in the way shown in FIG. 1. Such sieve baskets may be provided at the top, at the middle or at the bottom portion of the container. During the axial flow of the cellulosic pulp within the container the dewatering may be followed by dilution to, for instance, 1-5 percent, and repeated dewatering to about 8-15 percent by means of two successive sets of sieve baskets, when counting in the direction of flow of the cellulosic pulp. Alternatively the supplying of liquid may then take place by rotatable spray pipes in a known manner in accordance with the previously mentioned Swedish Pat. 198,496. During the dilution and, respectively, the dewatering steps the sieve holes may be kept clean by pressure surges with clean water, white water or some other suitable liquid.

A further object of the invention is that it should be possible to move the cellulosic pulp from one container to another (for instance, from one bleaching tower to a successive bleaching tower) without other dilution taking place than the one which might be obtained from a liquid treatment agent of the bleaching agent type, the condensate type etcetera.

The feeding of the cellulosic pulp may take place intermittently or shockwise, in which case no, or a limited, washing takes place during the feeding of the cellulosic pulp (in the direction of the arrow A).

Although unsuitable, in view of the power requirement and strength stresses, the sieve members (the col lecting chambers) 9, 10 may be given a vibratory motion in the axial and/or radial direction of the container 1, by which the liquid need not be pulsated by means of the special means described above. The sieve surfaces (i.e., the foraminous parts) of the sieve members may be parallel to the direction of flow of the cellulosic pulp, as shown in FIGS. 1, 3 and 4, or they may form an angle, to said direction.

As a summary it may be emphasized that the apparatus according to the invention is particularly suitable for the treatment by means of a liquid of suspensions of fibers or materials within the range of concentration of 1-15 percent.

What is claimed is:

1. Apparatus for the continuous treatment of a suspension of a fibrous material comprising a substantially vertical treatment container, means for introducing the suspension into one end of said container, means for moving the suspension axially through said container, said container being, in the part where the treatment is carried out, filled with the suspension, a plurality of supply means for introducing a treatment liquid into the moving suspension in said container, said supply means being positioned within the container and spaced transversely to the direction of movement of the suspension, a plurality of collecting chambers with foraminated walls for withdrawing liquid separated from the suspension, said collecting chambers being arranged stationarily within the container and spaced from the supply means transversely to the direction of movement of the suspension, the suspension filling the space therebetween, at least one pipe for passing the withdrawn liquid out of said container, at least one means for generating pressure impulses in a liquid, at least one means for transmitting the pressure impulses from said generating means to the liquid in said collecting chambers whereby the influx of liquid separated from the suspension into said collecting chambers may be periodically interrupted, entirely or partially, while substantially continuously passing the withdrawn liquid out of said container through said at least one pipe so that the fibrous material may not clog the foramina of the collecting chambers thus facilitating its passage axially through the container and means for removing treated suspension from the opposite end of the container.

2. Apparatus as claimed in claim 1 in which said means for periodically interrupting the influx of liquid comprises at least one conduit communicating with said collecting chambers and means for generating pressure impulses in said at least one conduit to be transmitted to said collecting chambers.

3. Apparatus as claimed in claim 1 wherein said supply means are rotatable about the axis of the container so as to supply treatment liquid in a rotating path to the suspension at substantially the same level as the collecting chambers.

4. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to said collecting chambers, for generating continuous pressure impulses.

5. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to said collecting chambers,

for eneratin continuous ra i d pressure impulses.

. Appara us as claime in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to said collecting chambers, for generating intermittent pressure impulses.

7. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to said collecting chambers, for generating at least one intermittent rapid pressure impulse at time controlled intervals.

8. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to the collecting chambers, for generating at least one intermittent rapid pressure impulse in said collecting chambers, each followed by a gradual decrease of the pressure therein. 

1. Apparatus for the continuous treatment of a suspension of a fibrous material comprising a substantially vertical treatment container, means for introducing the suspension into one end of said container, means for moving the suspension axially through said container, said container being, in the part where the treatment is carried out, filled with the suspension, a plurality of supply means for introducing a treatment liquid into the moving suspension in said container, said supply means being positioned within the container and spaced transversely to the direction of movement of the suspension, a plurAlity of collecting chambers with foraminated walls for withdrawing liquid separated from the suspension, said collecting chambers being arranged stationarily within the container and spaced from the supply means transversely to the direction of movement of the suspension, the suspension filling the space therebetween, at least one pipe for passing the withdrawn liquid out of said container, at least one means for generating pressure impulses in a liquid, at least one means for transmitting the pressure impulses from said generating means to the liquid in said collecting chambers whereby the influx of liquid separated from the suspension into said collecting chambers may be periodically interrupted, entirely or partially, while substantially continuously passing the withdrawn liquid out of said container through said at least one pipe so that the fibrous material may not clog the foramina of the collecting chambers thus facilitating its passage axially through the container and means for removing treated suspension from the opposite end of the container.
 2. Apparatus as claimed in claim 1 in which said means for periodically interrupting the influx of liquid comprises at least one conduit communicating with said collecting chambers and means for generating pressure impulses in said at least one conduit to be transmitted to said collecting chambers.
 3. Apparatus as claimed in claim 1 wherein said supply means are rotatable about the axis of the container so as to supply treatment liquid in a rotating path to the suspension at substantially the same level as the collecting chambers.
 4. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to said collecting chambers, for generating continuous pressure impulses.
 5. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to said collecting chambers, for generating continuous rapid pressure impulses.
 6. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to said collecting chambers, for generating intermittent pressure impulses.
 7. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to said collecting chambers, for generating at least one intermittent rapid pressure impulse at time controlled intervals.
 8. Apparatus as claimed in claim 1 wherein the means for periodically interrupting the influx of liquid includes means, connected to the collecting chambers, for generating at least one intermittent rapid pressure impulse in said collecting chambers, each followed by a gradual decrease of the pressure therein. 